Samples of blood, interstitial fluid, or other body fluids are commonly required for various medical purposes. For example, many diabetics must periodically monitor their blood glucose level to determine when an insulin injection is needed. Self-testing systems are available to enable a person to obtain a sample of his or her own blood, typically by penetrating the skin, and to subject the harvested blood sample to analysis of the blood glucose level. Often, a lancing device is used to penetrate the skin to obtain the required sample of blood. For example, U.S. Pat. Nos. 5,954,738; 5,879,311; 5,857,983; and 5,318,584 disclose particular forms of body fluid sampling devices.
In order to encourage compliance in regular usage, it is highly desirable that the use of a lancing device be as painless as possible to a subject obtaining a blood sample. Because the fingertips are rich in capillaries, a number of lancing devices have been designed for sample collection from this region. Nerve density is high in the fingertips, however, and significant pain often results from fingertip sampling. Moreover, repeated sampling can adversely result in callous formation on the fingertips. Accordingly, testing procedures have been developed allowing sampling at other sites on the body, such as the earlobe or forearm. By appropriate selection of the sampling site, the lancet geometry and the depth of penetration, the required sample size is obtained. According to present and developing sampling methods, sample sizes of about 8-10 microliters (.mu.L), and in some instances about 2-3 microliters (.mu.L), and possibly as little as about 400 nanoliters (nL) are sufficient for blood glucose analysis. It is anticipated that continuing developments in the field will progressively reduce the required sample size. In order to minimize pain and speed healing, it is desirable to minimize the size of the opening in the skin that is required to obtain a sample of the requisite size. To further reduce pain, it is also desirable that the lancing operation incorporate a quick penetration and retraction stroke, wherein the piercing instrument penetrates the skin and is quickly retracted along a substantially linear path.
It has also been found advantageous to provide a lancing device that is configured for ease of manipulation and use at different sampling sites. This is of particular importance with lancing devices intended for use by diabetics, as many diabetics suffer from poor eyesight and neuropathy, often resulting in reduced manual dexterity. Many previously known lancing devices have been found particularly difficult for such users to manipulate in carrying out certain sampling methods. For example, pen-shaped lancing devices are often too narrow for some users to grasp easily, and their cylindrical shape may render them difficult for some users to hold without unintentional twisting of the barrel of the device. Also, because such devices are typically relatively long compared to their width (or diameter) it is difficult for some users to apply sufficient pressure to maintain the device in a stable manner against the user's forearm during sampling. Other lancing devices incorporate non-symmetric or non-rectangular housings and/or housings with gripping surfaces or sample site contacting surfaces that are offset at oblique angles from the stroke axis of their lancets. Such devices are generally adapted for fingertip sampling, but are not well-suited for sampling at a site on the forearm. In particular, due to their angular offset, many users find it difficult to press these lancing devices against the forearm while maintaining the device in an orientation for lancing perpendicularly to the skin.
A number of previously known lancing devices enable penetration of the skin to a single, predetermined depth. Because of differences between individual users, such devices may generate a sample size larger or smaller than necessary. Accordingly it is desirable to provide a lancing device that enables easy adjustment of the depth of penetration, and that provides a reliable and accurate depth stop for providing a desired depth of penetration.
For purposes of commercial appeal to consumers, it has been found desirable to provide a lancing device that is compatible with standard, commercially available, disposable lancets. It is preferable that a standard lancet be readily mountable to a lancing device prior to use, and that the lancet also be readily and safely removable from the lancing device for deposit in a sharps container or other disposal canister. Particular forms of previously known lancing devices have incorporated an eject feature that permits a lancet to be "launched" from the device, potentially resulting in injury. Other known devices require the user to grasp the used lancet for removal, thereby presenting a risk of needle sticks. Accordingly, it would be preferable to provide a lancing device enabling safer and more controlled release of a lancet.
Certain previously known sampling devices provide for the application of pressure to tissue surrounding an incision to stimulate the formation of a drop of sampled fluid. The configuration of previously known stimulator members has been found to provide less than optimal sampling rates, to result in undesirable levels of user discomfort, and to result in bruising or marking of the skin with pressure indentations. In addition, it is often difficult to monitor the sample size produced during use of such previously known devices. Accordingly, it would be preferable to provide a lancing device providing improved stimulation of sample generation and easier monitoring of sample size.
Thus it can be seen that a need exists for an improved lancing device and methods for penetrating tissue to facilitate collection of a sample of a body fluid. It is to the provision of improved lancing devices and methods meeting these and other needs that the present invention is primarily directed.